1. Field of Industrial Utility
The present invention relates to a backlighting device for liquid-crystal panels that illuminates transmissive or semi-transmissive panels from the rear side.
2. Prior Art
Thin liquid-crystal displays provided with a backlighting mechanism that allows easy viewing of information on the screen are used with recent versions of laptop or book type word processors and computers. The backlighting mechanism in common use adopts a "single lamp edge lighting" method in which a linear light source such as a fluorescent tube is provided at one end portion of a transmissive light conducting plate as shown in FIG. 1(a), or a "dual lamp edge lighting" method in which a linear light source such as a fluorescent tube is provided at two end portions of a transmissive light conducting plate as shown in FIG. 2(a). As shown in FIGS. 1(b) and 2(b), one surface of the light conducting plate operating on those edge lighting methods is often covered partially with a light diffusing material and the thus covered area is almost entirely covered with a light diffusing/reflecting plate.
In addition, as is often the case today, backlighting devices are driven with a battery and a further improvement in the efficiency of power to luminance conversion is desired. To meet this need, it has been proposed that a light reflector covering the linear source be provided with a reflecting plate having high reflectance or that the area of the light conducting plate partially covered with the light diffusing material be provided with a reflecting plate having high reflectance. It is well known to utilize the Japanese Industrial Standard JIS K 7105, which was published in 1981, for testing and measuring the optical properties of plastic materials.
The methods described above achieve some improvement in the efficiency of power to luminance conversion but it is still insufficient and an even better improvement is desired.